An inertial navigation system (INS) includes at least a computer and a platform or module containing accelerometers, gyroscopes, and/or other motion-sensing devices. The INS is initially provided with its position and velocity from another source (a human operator, a GPS satellite receiver, and so forth), and thereafter computes its own updated position and velocity by integrating information received from the motion sensors. The advantage of an INS is that it requires no external references in order to determine its position, orientation, or velocity once it has been initialized. Thus, the INS can detect a change in its geographic position (a move east or north, for example), a change in its velocity (speed and direction of movement), and a change in its orientation (rotation about an axis). It achieves this by measuring the linear and angular accelerations applied to the system. Since it requires no external reference (after initialization), it is immune to jamming and deception.
While the INS is stationary, some ground based platforms (e.g., Radar and Forward Looking Infrared applications) need an accurate pointing solution from the inertial system since the target location is determined by using the range measurement received from Radar and the pointing solution (or heading) from the Inertial system. From the Target Location Error (TLE) point of view however, the pointing error is typically the dominant error source, contributing to about 70-80% of the total error budget for pointing solution accuracy. The solution or heading accuracy requirement for example, is usually 1 mil at 65 degree latitude, for example. In many instances, the stationary environment for the inertial system can last over days, weeks, or even months which can pose problems for determining accurate headings. Without the benefit of platform rotations for example, the inertial system heading tends to drift over time, resulting in system pointing performance degradation. In addition, the heading could exhibit erratic, out-of-tolerance excursions over the first 15-50 hours for long durations, for example (4-5 hours). An obvious solution is to improve the gyro performance such that the system heading can meet the required performance. This approach is expensive in both cost and time.